1. Field of the Invention
The present invention relates to molds for pattern transfer and methods for forming a resin pattern using them. It particularly relates to molds for fine pattern transfer and methods for forming a resin pattern using them in order to achieve fine pattern transfer with high accuracy at low cost by nanoimprint lithography.
2. Description of Related Art
In conventional processes for manufacturing semiconductor devices, etc., photolithographies are commonly used to form patterns of fine features. However, as the pattern size has continually decreased, they have presented a drawback of increased equipment and manufacturing cost, because, e.g., the pattern size has been limited by the wavelength of light used in the exposure, or an increasingly higher alignment accuracy has been required.
To address such problem, a technology of forming a fine pattern at low cost is disclosed in U.S. Pat. Nos. 5,259,926 and 5,772,905, etc. According to this technology, a desired fine pattern is transferred by pressing a stamper (forming member or mold) having the negative of a fine pattern of protrusions and depressions intended to be transferred against a resist film layer formed on a receiver substrate (transferred object). Particularly, it is described in the above-mentioned U.S. Pat. No. 5,772,905 that the nanoimprint technology can form a pattern of fine dimensions below 25 nanometers in one transfer.
FIG. 1 is a schematic illustration showing an example of a process flow chart for forming a fine pattern using a conventional nanoimprint technique. In this example, as shown in FIG. 1(a), a mold 101, and a transferred object 200 with a resin 202 for patterning applied on the surface of a receiver substrate (transferred object) 201, are each fixed on one of a pair of stages (not shown), the distance between which is controllable.
Then, the stages are actuated to press the mold 101 against the resin 202 so that the portion of the resin 202 facing a protrusion of the mold 101 is removed to expose the corresponding surface of the transferred object 201, thereby forming a resin pattern as shown in FIG. 1(b). When the film thickness of the resin 202 is larger than the height of the protrusion of the mold 101, a residual remains in a depression of the resin 202 as shown in FIG. 1(c). In such a case, the residual is etched by reactive ion etching or the like to expose the surface of the transferred object 201 at the depression of the pattern. In this manner, a resin pattern as shown in FIG. 1(b) can be obtained.
For example, the resin pattern thus obtained can be used as a mask to etch the exposed surface of the transferred object 201 as shown in FIG. 1(d) and then the resin 202 is removed, thereby forming a groove structure as shown in FIG. 1(e). For another example, as shown in FIG. 1(f), a metal film 203 or the like can be formed over the entire surface of the transferred object 200 and then the resin 202 is etched to form a structure having a predetermined pattern as shown in FIG. 1(g).
However, there still remain the following problems in nanoimprint technologies which are deemed to be capable of forming a fine pattern with high accuracy. For example, in FIG. 1(a), the transferred object 200 and mold 101 are each fixed on a stage; therefore, a high accuracy alignment between distant points is required, causing a possible productivity degradation or equipment cost increase.
On the other hand, there is a method in which the mold 101 is placed directly on the transferred object 200 (of course, vice versa is possible) rather than fixing them on stages. Typically, the resin 202 serving as a transferred object is heated up to about its glass transition temperature before a pattern transfer in order to secure flowability during the pattern transfer. This heating may release gaseous components remaining in the resin or degradation products from the resin as gas. The above-mentioned direct placement case presents a problem in that this gas remains between the depression of the mold 101 pattern and resin 202, degrading fine pattern transfer accuracy.